Fill Factor Losses in Cu2ZnSn(SxSe1−x)4 Solar Cells: Insights from Physical and Electrical Characterization of Devices and Exfoliated Films |
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| Authors: | Kong Fai Tai Oki Gunawan Masaru Kuwahara Shi Chen Subodh Gautam Mhaisalkar Cheng Hon Alfred Huan David B Mitzi |
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| Affiliation: | 1. Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore;2. Energy Research Institute @ NTU (ERI@N), Research Techno Plaza, Singapore;3. IBM TJ Watson Research Center, Physical Sciences Department, Yorktown Heights, NY, USA;4. Tokyo Ohka Kogyo Co. Ltd., Nakahara‐ku, Kawasaki, Kanagawa, Japan;5. Duke University, Durham, NC, USA |
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| Abstract: | Besides the open circuit voltage (VOC) deficit, fill factor (FF) is the second most significant parameter deficit for earth‐abundant kesterite solar cell technology. Here, various pathways for FF loss are discussed, with focus on the series resistance issue and its various contributing factors. Electrical and physical characterizations of the full range of bandgap (Eg = 1.0–1.5 eV) Cu2ZnSn(SxSe1?x)4 (CZTSSe) devices, as well as bare and exfoliated films with various S/(S + Se) ratios, are performed. High intensity Suns‐VOC measurement indicates a nonohmic junction developing in high bandgap CZTSSe. Grazing incidence X‐ray diffraction, Raman mapping, field emission scanning electron microscopy, and X‐ray photoelectron spectroscopy indicate the formation of Sn(S,Se)2, Mo(S,Se)2, and Zn(S,Se) at the high bandgap CZTSSe/Mo interface, contributing to the increased series resistance (RS) and nonohmic back contact characteristics. This study offers some clues as to why the record‐CZTSSe solar cells occur within a bandgap range centered around 1.15 eV and offers some direction for further optimization. |
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| Keywords: | solar cells fill factors nonohmic back contact secondary phases formation series resistance |
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